Coating compositions containing fluorocarbon polymer and aluminum borophosphate

ABSTRACT

A composition for priming a surface to improve the adhesion of a fluorocarbon polymer topcoat. The composition contains about 5090 percent fluorocarbon polymer by weight and 10-50 percent aluminum borophosphate by weight and a liquid carrier.

United States Patent Strolle Feb. 22, 197 2 [54] COATING COMPOSITIONS[56] References Cited CONTAINING FLUOROCARBON UNITED STATES PATENTSPOLYMER AND ALUMINUM BOROPHOSPHATE 2,562,118 7/1951 Osdal ..260/29.62,917,476 12/1959 Peterson et al. .....260/29.6 [721 invent: 51ml,spmgfield, 3 213,050 10/1965 Rice ..260/29.6 [73] Assignee: E. l. duPont de Nemours and Company,

Wilmington, Del. Primary Examiner-Harold D. Anderson Filed: Nov. 1969Att0meyJohn E. Gnffiths 21 Appl. No.: 873,633 [57] ABSTRACT Acomposition for priming a surface to improve the adhesion Cl 1 17/132 M,of a fluorocarbon polymer topcoat. The composition contains 2 1 F about50-90 percent fluorocarbon polymer by weight and [51 1 Int. Cl. ..C08f45/24 10.50 percent aluminum borophosphate by weight and a [58] Field ofSearch ..260/29.6 F, 29.6 RU, 33.4 F, i id -fl 7 Claims, N0 DrawingsCOATING COMPOSITIONS CONTAINING FLUOROCARBON POLYMER AND ALUMINUMBOROPHOSPHATE BACKGROUND OF THE INVENTION This invention relates tocoating compositions. It is specifically concerned with primercompositions for improving the adhesion of fluorocarbon polymer coatingsto their substrates.

The fluorocarbon polymer coatings when applied to metal, glass orsimilar type substrates have somewhat less then desirable adhesivetraits between the fluorocarbon polymer coatings and the substrate.Therefore, a need developed for a primer composition which would improveadhesion.

SUMMARY OF THE INVENTION This invention comprises a primer compositionconsisting of (1) particulate fluorocarbon polymer, (2) aluminumborophosphate and (3) liquid carrier. This primer composition is used toprime the substrate before the fluorocarbon 2 polymer topcoat isapplied.

The fluorocarbon polymers are known polymers. They include hydrocarbonmonomers completely or partially substituted with fluorine atoms or acombination of fluorine atoms and chlorine atoms. Included in this groupare polytetrafluoroethylene, copolymers of tetrafluoroethylene andhexafluoropropylene in all monomer unit ratios, and fluorochlorocarbonpolymers such as polymonochlorotrifluoroethylene.Polytetrafluoroethylene is preferred.

The aluminum borophosphate, Al O- ,-B O -P O composition is normally18-22 percent aluminum oxide, 8-12 percent boric anhydride, and 69-71percent phosphorus pentoxide by weight. The aluminum borophosphate isprepared by an oxide fusing process as is known in the art.

The liquid carrier may be water or an organic liquid miscible withwater, such as, ethanol, isopropanol, acetone or a Cellosolve. Water ispreferred.

The aluminum borophosphate ordinarily present in the compositionconstitutes about 10 percent thPough 50 percent by weight of thealuminum borophosphate and fluorocarbon polymer solids, preferably fromabout 25 percent through 35 percent.

The liquid carrier ordinarily present in the composition constitutesabout 5 percent through 50 percent by weight of the total compositionand preferably from about percent through 35 percent.

The composition can be made by mixing in an aqueous solution properamounts ofa fluorocarbon polymer and aluminum borophosphate or,alternatively, the procedure of Example 1 can be used. v

The resulting primer composition can be applied by spraying, brushing,dipping, or roller coating. If the surface to be coated is metal, it ispreferably pretreated by grit blasting, by the flame spraying of metalsor metal oxides, or by frit coating the substrate after application, theprimer coat is air dried and then baked at 450 F. for minutes.

This primer coat is then topcoated with a conventional clear orpigmented fluorocarbon polymer enamel, and baked in the usual way, togive an adherent fluoropolymer coating.

The composition is most useful for priming metal or glass cookware forcoating with polytetrafluoroethylene. This primer can also be used toprime many similar type articles for coating withpolytetrafluoroethylene. Polytetrafluoroethylene sheeting that has beenprimed with this material can be bonded to other materials such asmetals, plastics or glass.

As a specific example of the composition of this invention the followingillustrative examples are given. In these examples all parts are byweight.

EXAMPLE I A primer composition may be prepared by thoroughly mixing:

Al O;,P O,'l*l O (available as Monsanto's Alkophos) aluminum oxide 1 1%,phosphous pentoxide 36%, water 53% (47.1% solids) Boric acid dispersion(13.2%

boric acid and 31.8% pigment) (46.0% solids) in water 13.6 Surfactant(available as DuPonts Duponol) (30.0% solids) 2.1Polytetrafluoroethylene dispersion (60.0% solids) in water 61.2 Total:100.0

A physical mixing of Alkophos (Al O P O -H O) with boric acid producesaluminum borophosphate (Al O -P O -P O An aluminum sheet is cleaned. Thesheet is then sprayed with the primer composition to a thickness 0.2 to0.3 mil (dry). The sheet is then baked for 20 minutes at 450 F. afterwhich it is topcoated with a dispersion of polytetrafluoroethylenehaving the following composition:

Polytetrafluoroethylene nonionic Total: 100.0

The topcoat is sprayed over the primer to a total thickness of 1.2 to1.4 mils (dry) and then baked at 750 F. for 20 minutes.

The resulting coating of polytetrafluoroethylene adheres well to thealuminum substrate.

The invention claimed is:

1. A fluorocarbon primer composition consisting essentially of:

a. from 50 percent through percent by weight of particulate fluorocarbonpolymer;

b. from 10 percent through 50 percent by weight of aluminumborophosphate, the percentages by weight being based on the combinedweight of the solids of said fluorocarbon polymer and said aluminumborophosphate, said aluminum borophosphate being comprised of from 18-22percent aluminum oxide, 8-12 percent boric anhydride, and 69-71 percentphosphorous pentoxide by weight, and

c. a liquid carrier selected from the group consisting of water andwater-miscible organic liquids.

2. The composition of claim 1 containing from 65 percent through 75percent fluorocarbon polymer, 25 percent through 35 percent aluminumborophosphate and from 5 percent through 50 percent liquid carrier.

3. The composition of claim 1 wherein the fluorocarbon polymer ispolytetrafluoroethylene.

4. The composition of claim 2 wherein the fluorocarbon polymer ispolytetrafluoroethylene.

5. The composition of claim 1 wherein the aluminum borophosphate is inthe ratio by weight of 18.2 percent to 21.4 percent aluminum oxide, 8.6percent to 1 1.6 percent boric anhydride, and 70 percent phosphoruspentoxide based on the total amount of aluminum borophosphate.

6. The composition of claim 1 wherein the liquid carrier is water.

7. The composition of claim 2 wherein the liquid carrier is water.

2. The composition of claim 1 containing from 65 percent through 75percent fluorocarbon polymer, 25 percent through 35 percent aluminumborophosphate and from 5 percent through 50 percent liquid carrier. 3.The composition of claim 1 wherein the fluorocarbon polymer ispolytetrafluoroethylene.
 4. The composition of claim 2 wherein thefluorocarbon polymer is polytetrafluoroethylene.
 5. The composition ofclaim 1 wherein the aluminum borophosphate is in the ratio by weight of18.2 percent to 21.4 percent aluminum oxide, 8.6 percent to 11.6 percentboric anhydride, and 70 percent phosphorus pentoxide based on the totalamount of aluminum borophosphate.
 6. The composition of claim 1 wheReinthe liquid carrier is water.
 7. The composition of claim 2 wherein theliquid carrier is water.